Dimensional changes occur between structural members in response to expansion and contraction due to, for example, temperature changes, shortening and creep caused by pre-stressing concrete members, seismic cycling, vibrations, deflections caused by live loads, and longitudinal forces caused by vehicular traffic. An expansion joint gap is purposefully provided between the adjacent structural members for accommodating these dimension changes. These dimensional changes result in the expansion and contraction of the width of the expansion joint gap between the spaced apart structural members. Expansion joint systems are positioned within the expansion joint gap may to accommodate the movements in the vicinity of the gap, but still permit flow of traffic across the gap.
Cover plate expansion joints are one type of expansion joint system for bridging a gap between spaced-apart adjacent structural members. A cover plate expansion joint system includes a structural load bearing plate that extends across the expansion joint gap to cover the gap and anchors for engaging the cover plate to the underlying structural members. Generally, the cover plate extends from a first structural member to a second structural member. The cover plate overlies portions of the structural member on either side of the gap in order to support the cover plate. Vehicular traffic rides across the cover plate, passing from one roadway section to another spaced-part roadway section.
The cover plate is free to move in at least one dimension with respect to at least one of the structural members. The cover plate is separated from at least one supporting structural member with which it is free to move by some sort of sliding interface. Vertical motion between the structural members can rotate and stress the cover plate. These load stresses are large enough to damage the cover plate, pull out anchors, cause fatigue damage near anchor holes, or otherwise damage the expansion joint system.
When traffic travels over the cover plate, it downwardly loads the plate and causes the plate and structure to deflect downwardly. In conventional cover plate systems, there is either no or very little plate rotational capacity. The result is that traffic traveling over the plate loads the plate causing the plate and structure to deflect. This creates “plate slap” as the plate impacts the supporting structural member. As the traffic moves away from the cover plate, the cover plate is unloaded thereby allowing the strain imparted to the cover plate and structure to be released. The release of the strain on the cover plate sometimes creates “plate bounce” as the deflected plate springs back into position. Both plate slap and plate bounce are generally undesirable, not only because they create unnecessary noise and vibration, but because they are symptomatic of operation which can harm the expansion joint system.
While cover plate expansion joint systems have achieved acceptance by structural engineers, they suffer from the above mentioned performance shortcomings. Accordingly, it remains desirable to provide a cover plate expansion joint system which can accommodate traffic without the resultant plate slapping or plate bouncing, and also minimizes fatigue failure near anchor holes, lack of impact absorption, inability to accommodate vertical offset between adjacent structural members, pull-out of anchors, and spalling and cracking of concrete in header regions of the system.